Gunfire control system for supplying aiming information for guns having different ballistic characteristics



March 12, 1968 D. M. COOPER ET AL 3,373,263

GUNFIRE CONTROL SYSTEM FOR SUPPLYING AIMING INFORMATION FOR GUNS HAVINGDIFFERENT BALLISTIC CHARACTERISTICS Filed Feb. 27, 1946 I0 I DIRECTOR3I\ I I G POWER Br MOTOR l AMPLIFIER I Eb 2 I 28 33: 32 1 VARIABLE FIXEDl RATIO RATIO 3 MULTIPLIER MULTIPLIER i l J '4 H on Hv:

4 n, '6 suns 24 l9 20 I i INVENTORJ E DENSIL M. COOPER CHARLES F. WYSONGl8 THOMAS W. C APPELLE ATT RNEY 3,373,263 Patented Mar. 12, 19683,373,263 GUNFHRE CONTRGL SYSTEM FOR SUPPLYING Alh IING KNFORMATION FGRGUNS HAVING DIFFERENT BALLISTIC CHARACTERISTECS Densil M. Cooper,Washington, D.C., Charles F. Wysong, Atlanta, Ga, and Thomas W.Chappelle, US. Navy, assignors to the United States of America asrepresented by the Secretary of the Navy Filed Feb. 27, 1946, Ser. No.650,584 2 Claims. (Cl. 235-615) This invention relates to gunfirecontrol systems and in particular to fire control direction and computersystems which may be employed to provide gun pointing data for guns ofvarious sizes.

In numerous circumstances, typically aboard warcraft, it is desirable toemploy guns of various sizes and control their fire by means of a singledirector and computer system. Computer systems as presently employed areusually designed for a particular size and caliber gun because of thecomplexities involved were a single computer system to be set-up for theaiming of guns of a plurality of sizes.

It is therefore an object of the present invention to provide meanswhereby a fire control computer system designed for one size gun may beemployed to give suhstan tially accurate gun aiming data for guns of aplurality of s1zes.

Another object of the present invention is to provide in a gunfirecontrol system, a method of altering the information supplied to thecomputer by the director so that the gunfire control system can be madeto provide substantially accurate aiming information for any one of aplurality of guns having different ballistic characteristics.

Another object of the present invention is to provide a gunfire controlsystem capable of supplying substantially accurate aiming informationfor a plurality of guns having different ballistic characteristics.

Other and further objects and features of the present invention willbecome apparent upon a careful consideration of the following detaileddescription when taken together with the accompanying drawings whichillustrate a typical embodiment of the invention and the manner in whichthis embodiment may be considered to operate.

In the drawing:

FIG. 1 shows one embodiment of the features of the present invention;

FIG. 2 shows a simplified fire control problem as encountered and solvedwith the apparatus of FIG. 1 for guns having different ballisticcharacteristics.

In accordance with the general features of the present invention, asystem of gunfire control is provided which is capable of accurate gunaiming information for a first gun having certain ballisticcharacteristics and of substantially accurate aiming information for asecond gun having different ballistic characteristics. A standard firecontrol computer of conventional design having information or signalinputs and designed to provide aiming information for the first gunemployed. When calculation for the second gun is desired, certain of theinput signals are modified by new apparatus according to the teachingsof the present invention to cause the computer to solve a fictitiousproblem for the first gun which will cause the production ofsubstantially accurate aiming information for the second gun.

For convenience, the following symbols for shipboard fire control asemployed in the specification, are defined.

B'gr (gun train order): The angle between the fore and aft axis of ownship and the plane through the gun perpendicular to the deck (plusparrallax correction if made), measured in the deck plane clockwise fromthe bow. (Gun train is the ordered gun train as transmitted to the gun.)

Br (director train): The angle between the fore and aft axis of own shipand the vertical plane through the line of sight from the director,measured in the deck plane clockwise from the bow.

dH (rate of climb): The time rate of change of height of target.

Dj: Spot correction in gun deflection angle made in the slant plane tothe target.

Eb (director elevation): The elevation angle of the director line ofsight above the deck (plus parallax correction if made) measured in thevertical plane through the line of sight to the target.

E'g (gun elevation): The elevation angle of the gun above the deck (plusparallax correction, if made) measured in the plane through the gunperpendicular to the deck. (Gun elevation order is the gun elevationtransmitted to the gun.)

F (fuse setting): Fuse setting in seconds.

R (range): The distance from the director to the target (measured alongthe line of sight).

R (virtual target range): Approximately equal to target range Rmultiplied by factor equal to the reciprocal of the ratio of the time offlight of the projectile for the gun for which the control system givesaccurate solution T to the time of flight of the projectile for the gunfor which the control system gives substantially accurate solution Tboth flight times taken for the same range. The value of virtual targetrange R is approximately related to the actual target range R accordingto the equation below.

This relationship is a first approximation and should subsequently bemodified empirically in accordance with the height H to become moreaccurate. Such modification is provided by apparatus combination inaccordance with the teachings of the present invention.

R (predicted virtual target range): Predicted virtual range of target atinstant a projectile, fired at the present time, reaches the targetvicinity.

H (height): The vertical distance of the target above the horizontalplane through the director.

H (virtual target height): The value of the virtual target height H isthat value of H obtained from the computer when it is provided with R asinput in place of the conventional R input. It can be shown that thisvirtual target height is approximately equal to target height Hmultiplied by a factor equal to the reciprocal of the ratio of the timeof flight of the projectile for the gun for which the control systemgives accurate solution T to the time of flight of the projectile forthe gun for which the control system gives substantially accuratesolution T both flight times taken for the same range. By way ofexample, from the above definitions we know that,

. H v Sln. (E E -R which can be rewritten as H =R sin (E substitutingfor R H R sin (E f1 but R sin (E =H therefore Sa (air target air speed):Speed of air target along the line of flight with respect to the earth.(May or may not be for horizontal flight.)

V Spot correction in gun elevation angle made in a plane perpendicularto the horizontal plane.

With reference to FIG. 1, a gunfire control system is shown in which adirector 10 is employed to secure positional data regarding theinstantaneous range, elevational angle and bearing of a distant target.This data is supplied to a computer system in the form of signals whichmay be of mechanical movement or electrical variation such as shaftdisplacement or rotation, fluid pressure variations, or amplitude,frequency, or phase electrical variations. The computer system includesa main computer unit 11 and an auxiliary unit 12. Aiming information issupplied to the guns 13 from the computer 11 which permit orientation ofthe guns so that the path of a shell leaving any of them at one instantwill intersect the path of the target at the instant in time at whichthe target is at the point of intersection.

The computer 11 is of any suitable conventional type designed primarilyfor the control of a gun having certain ballistic characteristics. As anexample of a typical computer, reference is made to the US. patent toChalice et al., 2,340,865 wherein is described a computer which requiresa separate height finder. For the purposes of the present invention, aset-up may be considered wherein the computer of Chalice et al.,together with a height finder, both responsive to input signals from thedirector 10 of FIG. 1 are included as components of block 11. Where thecomplete system is mounted aboard ship it is preferably adapted toreceive three primary input signals from the director Br, Eb, and R. Tothis information is ordinarily added but not shown in FIG. 1,conventional input signals relative to the motion of the structure orship carrying the fire control system and of the air conditions. Withsome types of computers it is necessary to supply additional inputsignals which may in many instances be done manually. The exact mannerof supplying the additional information is of no real significance tothe present invention, the only important thing being that the computer11 be of the type suitable to receive target position information from adirector 11 and supply control information to accurately direct the fireof guns of block 13. To assist in this operation, certain types ofcomputers may require additional information inputs such as informationregarding estimated target motion 8:: and dH which can be introducedmanually for example through controls 14 and 15, and spot correctionsintroduced manually in response to observations of accuracy of the shellhits. Such spot corrections may be introduced as D and V through thetypical controls 16, 17. The principles of the present invention areequally applicable Where the computer 11 is adapted to make furtherconventional corrections such as trunnion tilt, parallax, gun erosion,and others.

The principal output quantities of the computer 11 are B'gr, Eg, and F,which are supplied to the guns, and H or 1-1,, obtained in the course ofcalculation of the particular fire control problem.

Unit 12 is employed where it is desired to obtain aiming data for gunshaving ballistic characteristics dissimilar to those for which theoriginal computer system 11 was designed. A primary function of theadapter unit 12 is to alter the range signal R delivered to the computer11 from the director 10 whenever computation is desired for a second gunhaving characteristics different from those of a first gun for which thecomputer 11 was designed. This range signal alteration is made to causethe computer 11 set-up to provide accurate solution of a problem for thefirst gun to solve a fictitious problem which will supply substantiallyaccurate firing information for the second gun.

Referring now to FIG. 2, the method by which the fictitious problem isset up and solved is shown For this part of the discussion, straightline shell paths without l arched trajectory have been chosen. Theposition of the platform or ship mounting the gunfire system is at point18. The horizontal plane is that of 13, 19, 21 The problem is to securefiring information for a target presently located at point 21 andtraveling in the direction 21-22 such that a shell fired at the instantthe target is at position 21 will strike the target when it reachesposition 22. Estimates of the target speed Sa and rate of climb dl-l canbe supplied manually to the computer 11 of FIG. 1 by means of controls14, 15, respectively. Accurate firing information is readily obtainedfrom the computer 11 for the gun for which the computation system wasdesigned. For a gun having different ballistic characteristics, forexample, one firing a larger diameter and larger weight shell which willhave different characteristics such as initial velocity, rate of changeof velocity with distance traveled, and drift per unit distance oftravel, the firing information supplied for the first gun would notsufiice. To obtain substantially accurate information for the secondgun, the target range signal R which is represented by the line 18, 21is multiplied by a factor to obtain a virtual target range signal Rwhich is represented by the line 18, 23. This virtual range signal isthen transmitted to the computer 11 and employed as a basis forcalculation of firing data to obtain a predicted virtual target position24, which, when fired upon by the second gun will cause simultaneousoccupation of point 22 by the projectile and the target. The factor bywhich the range signal R is multiplied to obtain the virtual rangesignal R is equal to the reciprocal of the ratio of the time of flightof a projectile from the first gun to point 22 to the time of flight ofa projectile from the second gun to point 22. This ratio issubstantially constant regardless of the actual distance 18-22 or 1821and for practical purposes may be considered constant for any reasonablecombination of guns. It is to be noted that the vector 23, 24, is in thesame direction as vector 21, 22, but that its length bears the samerelationship to vector 21, 22 as the distance 18, 23 does to distance18, 21. Thus the Sn and dH estimates must be altered (manually) by thesame factor as the range R. All angular measurements such as lead angle21, 18, 22 and predicted elevation angle 22, 18, 2!) are unaffected bythe change in range.

In practical fire control situations wherein the projectiles do nottravel in straight lines but rather have arched trajectories, the simplerange alteration as given above is not entirely satisfactory. A firstcorrection that is made is that of altering the virtual target rangesignal R by another factor depending upon H (distance 23, 25) asobtained from the computer 11 of FIG. 1 in solving the triangle 23, 18,25'.

The above correction for shell trajectory is not altogether sufiicientfor all target ranges, hence a second correction must be made.Furthermore, the windage and drift while in flight are generallydifferent for different size projectiles. The supplemental corrections,for drift, windage, and trajectory are small and are best grouped intoan indefinite classification called spot corrections signals, which aremade manually while firing is in progress. These spot correctionssignals are designated V; and D, and are introduced by controls 16 and17, respectively, of the computer system 11 in FIG. 1. They areconveniently made by resetting controls 16, 17 by known, substantiallyfixed amounts depending upon target range When computation for differentguns is desired. To this end, a plurality of scales, in this case two,is provided for each of controls 16, 17, with the appropriate change in.scale employed when operation is changed from calculation for one gun tocalculation for another.

Referring again to FIG. 1, the range input signal from the director 16to the adapter 12 is applied to a two position switch 27. With switch 27connected to contact 28, the target range signal as obtained by thedirector 16 is supplied direct to the computer 11 for operation with thegun for which the computer 11 was designed. With switch 27 connected tocontact 29, the range signal obtained from the director is applied to apower amplifier 30 which supplies controlled power for imparting motionto the armature of an electric motor 31. Motion of the shaft of motor 31is applied to a fixed ratio multiplier 32. The ratio of the multiplier32 is chosen such that true target range represented by the distance1821 in FIG. 2 will be multiplied by a constant value to obtain thevirtual target range 18-23 which will drive the computer 11 to solutionfor the second size gun for the actual target at range 18, 21.

In conventional remote signal conveying systems for this type ofapplication it is common practice to employ selsyn or synchro systemswherein the position of a movable mechanical member or shaft located atone point is converted into electrical signals which cause correspondingmechanical motion of a shaft at a distant point. Such remote indicatorsare familiar to those skilled in various electrical arts, and inparticular are widely used in radar where the orientation of a rotatabledirectional antenna located at one point must be repeated or analyzed atanother point. This selsyn or synchro system is ideal where theindicating point does not require much power because any power requiredfor the rotation of the indicator, as Well as frictional losses andcertain resistance losses must be provided by the distantly locatedmovable system. In certain instances this power loss is negligible, inothers it is undesirable because of the greater possibility ofintroduction of erroneous indication. To provide power where theindicating system requires it and hence to improve accuracy, a servotype system may be employed in which the indicating device is driven bya separate power source which is merely synchronized with the remotedevice through the selsyn or synchro system. In such a layout,therefore, error signals are derived in dependency on positionaldifferences between the internal indicating system and the remotemember. These error signals are amplified by the power amplifier 30 andthen employed to drive an electric motor 31 which positions theindicating shaft directly. It should be remembered, however, that theelectrical system herein indicated, although highly desirable, is notessential to the performance of the invention, it being entirelypossible for the principles of the present invention to be realizedsatisfactorily by employing mechanical linkage in which case the switch27 would become a gear shifting mechanism.

With range signals thus delivered to the device 12 bv any suitable orconvenient means, they are acted upon by the fixed ratio multiplier toobtain the virtual range signals R By Way of example the fixed ratiomultiplier 32 is a fixed ratio gear train operative to receive input atone angulan'ty and change it to a second angularity.

The simple R signal from the multiplier 32 is modified additionally invariable ratio multiplier 33 in dependency on the H of the target asobtained from the computer 11. Although height of target information isnot made use of in some computers, it is a relatively simple expedientto provide a height computer which furnishes the desired heightinformation in response to elevation and range inputs. This is typicallyaccomplished by mechanically solving the equation SID. (E E Such heightcomputers are well known in the art. Therefore, since the director 10provides range R and elevation E signals directly, computer 11 mayconveniently include or be modified to include a height computer whichsupplies a height signal to multiplier 33 in response to and independency on the target elevation E, and range input signals providedby director 10 and supplied to the computer 11. The linkage supplying Hto the variable ratio multiplier 33 may be mechanical, electric, ormanual as referred. A variable ratio device such as the variable speeddevices 13, 74, etc. of the US. patent to Chaffee et al. 2,340,865 wouldbe suitable. Should a cylinder, ball and disc type device, such as shownin Chaifee et a1- be used, the signal from the fixed ratio multiplier 32could be applied to the disc, the virtual height signal H from computer11 would position the balls and the output signal R would then be takenfrom the cylinder. Of course, the invention is not intended to belimited to the above described variable speed device and other variableratio multipliers, such as a screw type multiplier, could also besatisfactorily used.

In operation, the fire control system may be quickly changed to givesolution for a plurality of gun ballistic characteristics by operationof switch 27 and the resetting of controls 14, 15, 16, 17.

From the foregoing discussion it is apparent that considerablemodification of the features of the present invention are possible andwhile the device herein described and the form of apparatus for theoperation thereof constitutes a preferred embodiment of the invention,it is to be understood that the invention is not limited to this precisedevice and form of apparatus, and that change may be made thereinwithout departing from the scope of the invention as defined in theappended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. A gunfire control system for controlling the fire of any one of aplurality of guns having dissimilar ballistic characteristics,comprising; a director and a computer system for supplying accuratefiring information for a first gun having certain ballisticcharacteristics, said director supplying signals including target rangeto said computer system, means altering the target range signal suppliedto the computer when a second gun having different ballisticcharacteristics is employed, said last named means altering the targetrange signal in accordance with the relationship of the ballisticcharacteristics of the first gun to those of the second gun to generatea range signal in accordance with a fictitious target, and means furtheraltering the target range signal supplied to the computer system by avariable amount dependent upon the product of target height multipliedby said relationship to partially compensate for any difference intrajectory ballistic characteristics of the two guns.

2. A fire control system for selectively controlling a plurality of gunshaving dissimilar ballistic characteristics, comprising a director forproviding target bearing, elevation and range signals, a computerresponsive to signals derived by the director for positioning a firstgun of selected characteristics, and a signal alteration apparatusinterposed in the path of range signals from the director to thecomputer when the system is to be used for positioning a second gun ofcharacteristics different from the first, said apparatus comprising ameans for altering director derived range signals in proportion to theratio of the time of flight of a projectile for the second gun to thetime of flight of a projectile for the first gun, said signal alterationapparatus also comprising a means for altering additionally the rangesignals by a variable amount which is dependent upon the product oftarget height multiplied by said ratio.

2,409,648 10/ 1946 Van Auken.

MALCOLM A. MORRISON, Primary Examiner.

MAX L. LEVY, B. H. CARPENTER, J. B. LEWIS,

Examiners.

2. A FIRE CONTROL SYSTEM FOR SELECTIVELY CONTROLLING A PLURALITY OF GUNSHAVING DISSIMILAR BALLISTIC CHARACTERISTICS, COMPRISING A DIRECTOR OFPROVIDING TARGET BEARING, ELEVATION AND RANGE SIGNALS, A COMPUSTERRESPONSIVE TO SIGNALS DERIVED BY THE DIRECTOR FOR POSITIONING AND FIRSTGUN OF SELECTED CHARACTERISTICS, AND A SIGNAL ALTERNATION APPARATUSINTERPOSED IN THE PATH OF RANGE SIGNALS FROM THE DIRECTOR TO THECOMPUTER WHEN THE SYSTEM IS TO BE USED FOR POSITIONING A SECOND GUN OFCHARACTERISTICS DIFFERENT FROM THE FIRST, SAID APPARATUS COMPRISING AMEANS FOR ALTERING DIRECTOR DERIVED RANGE SIGNALS IN PROPORTION TO THERATIO OF THE TIME OF FLIGHT OF A PROJECTILE FOR THE SECOND GUN TO THETIME OF FLIGHT OF A PROJECTILE FOR THE FIRST GUN, SAID SIGNAL ALTERATIONAPPARATUS ALSO COMPRISING A MEANS FOR ALTERING ADDITIONALLY THE RANGESIGNALS BY A VARIABLE AMOUNT WHICH IS DEPENDENT UPON THE PRODUCT OFTARGET HEIGHT MULTIPLIED BY SAID RATIO.